1. Field of the Invention
The present invention relates to a backlight module, and more particular to a backlight module that reflects a light source to a light guide plate by a multiple reflection.
2. Description of Prior Art
Since light crystal display (LCD) is not a self-emitting display device, an external light source is mandatory for achieving the display effect. Most liquid crystal displays adopt a backlight module to provide a uniform liquid crystal display panel and a high-brightness light source. The basic principle of the LCD adopts a spot light source or a linear light source, and effectively converts the spot or linear light source into a planar light source to provide a product emitting a planar light source with high brightness and uniform luminance.
In general, a backlight module can be divided into two types: a front light type and a back light type, and the back light type can be classified and developed into the following structures by their specifications and the positions of the lamps:
1. An edge lighting structure as shown in FIG. 1 sets a cold cathode fluorescent lamp 1a on a lateral side of a light guide plate 2a, and the light guide plate 2a adopts an injection molding printless design and the edge lighting structure is generally used in small or mid-size backlight modules below 18 inches, and an edge lighting light source design comes with a lightweight, thin, narrow-framed, and low power consumption features, and thus it can be used as a light source for mobile phones, personal digital assistants (PDAs) and notebook computers.
2. A bottom light structure as shown in FIG. 2 installs a cold cathode fluorescent lamp 1a at the back of the light guide plate 2a. Due to the super large backlight module, the edge lighting structure no longer maintains its advantages on weight, power consumption and brightness anymore, and thus the bottom light structure that installs the cold cathode fluorescent lamp 1a at the back of the light guide plate 2an is developed. The bottom light structure is applicable for portable LCD monitors and LCD TVs with relaxing requirements.
In recent years, light emitting diode (LED) becomes increasingly popular due to its compact size, low power consumption and long life expectancy, and it gradually takes over the traditional light bulb. For instance, LED is used extensively in traffic lights, automobile signal lights, flashlights, mobile phones, lamps and large outdoor billboards. Some light sources of the present backlight modules also adopt LED as a light source, and the LED 3 is usually installed on a lateral side or a backside of the light guide plate 2a as shown in FIGS. 3 and 4.
In fact, the heat source produced by an electrically connected LED 3a will affect the light emitting efficiency of the LED, and insufficient heat dissipation will cause the LED 3a unable to meet its specifications. To solve the aforementioned problem, some manufacturers reduce the input current (which is known as load reduction) to 60% of the specified value, so that the brightness of each LED 3a will fall below 60% of the specified value. More light emitting diodes are added to satisfy the brightness requirement, but such arrangement makes the manufacture more complicated and incurs a higher cost.